1. Technical Field
The present invention relates to a hybrid excavator that charges an electrical energy storage device with regenerative power generated by an electric load.
2. Description of Related Art
Generally, in hybrid excavators, a DC bus is positioned between an electric load and an electrical energy storage device corresponding to a power supply, and electric power is supplied to the electric load via the DC bus. By controlling the voltage of the DC bus using an up-down voltage converter, a supply of electric power from the electrical energy storage device (discharge) and a supply of electric power to the electrical energy storage device (charge) may be controlled.
The voltage of the DC bus varies depending on the operating state of the electric load. Considering demands to improve the efficiency of the up-down voltage converter, the voltage of the DC bus is preferably positioned to fall within a certain range. Accordingly, an electrical energy storage unit is known that includes a constant voltage electrical energy storage part which maintains a voltage level within a fixed range, and a variable voltage electrical energy storage part which permits variations in the voltage level due to motor power regenerating operations of the electric load.